Quasi-3D mapping of soil moisture for agriculture using electric conductivity sensing

<p>Knowledge of real time spatial distribution of soil moisture has great potential to improve yield and profit in agricultural systems. Rapid and precise quantification of water in crop fields is challenging due to the influence of highly variable soil properties such as texture and porosity.  Recent advances in non-invasive electromagnetic induction (EMI) techniques have created an opportunity to determine soil moisture content with high-resolution and minimal soil intrusion. So far, EMI has mainly been validated for homogenous soils, which are not common in agriculture. This study from a field site in Western Australia converts time series apparent electrical conductivity data recorded with a Dualem 1Hs EM-meter into spatiotemporal domains. A least square inversion algorithm was used to determine electric conductivities for individual soil layers (0-50cm, 50-80 cm and 80-160 cm) for two EMI surveys at a trial site, with different crop rotations and varying moisture conditions. A laboratory experiment under controlled conditions developed electric conductivity vs volumetric water content relations with power law functions for each layer with R<sup>2</sup> values between 0.98 and 0.99. Subsequently, EMI data were converted to volumetric water contents for each layer and predictions were spatially displayed. These EMI soil moisture predictions were compared with neutron moisture meter measurements, with R<sup>2</sup> values between 0.95 and 0.74 for the two surveys. The method is robust and offers a comparatively fast method to estimate the soil moisture status in fields and to subsequently make informed management decisions. </p>

Factory-Calibrated Soil Water Sensor Performance Using Multiple Installation Orientations and Depths

The use of soil water sensors is commonly advocated to aid and improve irrigation management in crop production systems. However, there are concerns about how sensor type, installation technique, sensor orientation, and soil texture may affect sensor accuracy. A field study was conducted to compare the performance of three commercially available soil water sensors (Acclima 315L, Decagon GS1, and Campbell Scientific 655) and a soil water potential sensor (Watermark 200SS) using different installation orientations of horizontal insertion, laid horizontal placement, and vertical insertion at depths of 15, 46, and 76 cm (6, 18, and 30 in.) in an irrigated clay loam soil field. Results indicated all sensors demonstrated similar trends of soil water content in response to wetting events (precipitation and irrigation) at the 15 cm depth following a 4-month settling period prior from the start of the growing season. Comparatively, the Acclima 315L performed well using horizontal insertion compared to calibrated neutron moisture meters (NMMs) at depths of 46 and 76 cm with R2 of 0.73 and 0.96 and slopes of 1.36 and 1.47, respectively. In addition, water storage in the 0.9 m soil profile integrated using the horizontally inserted Acclima 315L across the three depths matched closely with profile water storage determined by the NMMs with a mean difference (MD) and root mean square error (RMSE) of 25.7 and 36.4 mm. However, site-specific corrections or calibrations for each sensor type are required for accurate soil water content estimations with this clay loam soil for irrigation management applications. Keywords: Corn, Irrigation management, Neutron moisture meter, Soil water content, Soil water sensors, Semi-arid region.

Soil Water Sensor Performance and Corrections with Multiple Installation Orientations and Depths under Three Agricultural Irrigation Treatments

Performance evaluations and corrections of soil water sensors have not been studied using different installation orientations under various irrigation treatments in the Texas High Plains. This study evaluated the performance of four sensors using factory calibration and derived field corrections as compared to calibrated neutron moisture meters (NMMs). Sensor performance was assessed using horizontal insertion, laid horizontal placement, and vertical insertion at 15.2, 45.7, and 76.2 cm depths in a clay loam soil with three irrigation treatments. Results indicated the factory-calibrated Acclima 315 L performed satisfactorily using horizontal insertion as compared to NMM measurements at 45.7 and 76.2 cm depths with a ±2% mean difference (MD) and <3.5% root mean square error (RMSE). The factory-calibrated Acclima 315 L using horizontal insertion also performed satisfactorily across all irrigation treatments according to soil profile water storage (MD = 0.36% and RMSE = 3.25%). Generally, the factory-calibrated Decagon GS1 and Campbell Scientific 655 using vertical insertion agreed more closely with NMM measurements compared with other installation orientations. There was a significant underestimation of water storage (>60 mm) in the 0.9 m soil profile using the Watermark 200SS. In summary, field corrections are required for Decagon GS1, Campbell Scientific 655, and Watermark 200SS sensors.

In memoriam: Professor Gérard Seguin

On April 13, 2019, Professor Gérard Seguin passed away at the age of 82. Professor Seguin was a creative and enlightened researcher and a much respected professor in soil and terroir sciences at Bordeaux University. Encouraged by his mentor, the late Emile Peynaud, he developed a whole new field of research on the influence of soil and climate on vine development, grape composition and wine quality, referred to as “terroir”. As early as 1969 he published a paper in which restricted but regular water supply to the vines was shown to be a key factor in wine quality, a result which has been confirmed by many researchers ever since (Seguin, 1969). In this study, the water uptake of the vines was quantified with a neutron moisture probe, a highly innovative technique for that time. Unfortunately, this ground-breaking paper came out in a period when most European researchers published in their own language. Only in 1986 Seguin published a review paper about the effect of terroir in viticulture in English (Seguin, 1986). Seguin was also convinced that high terroir expression is only possible when grapes ripen at the end of the growing season, in relatively cool conditions (van Leeuwen and Seguin, 2006). This concept is gaining importance as the climate warms up. Seguin was one of the first researchers to study terroir on a scientific basis and certainly the very first to understand that its effect can only be understood by a multi-disciplinary approach, considering interactions between the climate and the vine and the soil and the vine. After his retirement in 1998, he was happy to see that terroir is gaining international recognition as an important aspect in winegrowing, as shown by terroir conferences organized all around the world, in Davis California in 2006, in Oregon in 2016 and one scheduled in Adelaide in 2020.Gérard Seguin was also a highly respected professor, unanimously appreciated by his students. He took his teaching mission very seriously, spending hours on fine tuning his lectures. He was able to explain complex issues in soil science in a perfectly clear way. He was close to his students and always ready to take their defense. In the management of his lab, he left as much freedom as necessary to his staff and doctoral students to develop innovative research, but he imposed everyone to be present at the coffee break of 9 am. This was not only a moment to discuss private matters and share impressions about last night’s good bottles, but also a place where many good research ideas emerged. This is certainly a point to consider in our ever busier schedules, where time for social interactions is more and more limited. We are sad to say farewell to Professor Seguin but we are grateful for his tremendous legacy.